Omar Aziz started stealing bikes when he was 17 and carried on until he finally weaned himself off crack cocaine at the age of 29. Now he wants to make amends. He is volunteering in his local area and he agreed to advise Guardian readers how not to get their bikes stolen.

Aziz stole a lot of bikes to feed his habit: "When I sell one thing I go and buy my drugs, smoke it, when it finishes, I have to go and get more. I nick another bike," he said.

The easiest pickings were bikes secured with cheap locks. "Some people think they don't have enough money and they buy thin locks, and I used to go and just push the bike and pull it and the lock will break."

Today Aziz locks his own bike up with two thick chains, through both wheels and the frame. Thieves can get through thick chains with the right equipment but it takes a lot of time and heavy cutting equipment. But even that didn't always deter him. On at least one occasion, having eyed-up a bike, Aziz first stole tools before going back for the bike.

CCTV it seems, is also no deterrent. "Even if there is cameras they don't care. For me the best place is to leave your bike is a place where there are people around."

But even the busiest streets empty out eventually, so if Aziz really wanted a particular bike he would damage a tyre so the owner would leave it in the rack for longer. "Someone, if they find their tyre punctured they should take their bike with them, right at that minute because someone has done it on purpose to come and take it after."

Owners of bikes costing more than a few hundred quid should always take them indoors. Whenever Aziz's crack dealer got wind of an expensive bike locked up in the area he would send Aziz out to fetch it. Thieves also watch where expensive bike are regularly parked. For anyone with outdoor parking, he recommends riding a cheaper bike.

Aziz himself also chose to steal the more expensive bikes just to ride them as far as the sale point, regardless of the fact that he was rarely paid more than £20-30 for any bike he stole – the price of a few rocks of crack cocaine. "I used to steal the £800 bike when I need the rock and sell it for £20 pounds. Sometimes I was very desperate."

"I take them to pubs, coffee shops, kebab shops. People buy them and know that I'm a crack head and they say he's a crack head, give him a tenner, give him 20 and they sell it."

In London, Aziz found stolen bikes were particularly easy to sell. "There is a really slight chance of you getting caught when you are nicking bikes. You just crack it, get on it, gone. When they nick bikes they paint them ... you don't even know it's your bike. [In London] no one is going to know, they are not going to stop you...You can steal from north London and go to west London and you're alright."

Aziz says he feels bad about the things he did while he was an addict. "I know its bad, you know. That's why I'm doing voluntary work to give something back. I feel bad you know. I didn't do it just to keep it for myself. I done it to feed my habit."

Two weeks ago Aziz had his own bike stolen while he was buying cigarettes from his local shop. He started to call the police but gave up when his credit ran out and decided to catch the thief himself instead. "I left it outside the shop for 10 seconds just to buy cigarettes. I come back out and my bike is gone."

"I felt very very very very angry when my bike got stolen. If I'd caught the man who stole it that minute. I don't know what I could have done, honestly. But I caught him a week later and he said to me he bought it for £2.50. But then I said what goes around comes around."

It took Aziz just days to find his stolen bike. "For me its been stressful. Honestly. He was on crack. I could see it in his face that he was in a bad way and I felt sorry. I thought what am I going to do to him. But people can't help it. They see your bike and ... you give them any chance and they will take it. It's not safe, it's not safe at all. Everywhere you go lock your bike."

• Omar Aziz is not the ex-bike thief's real name and he was not paid for speaking to the Guardian